This disclosure generally relates to plastic compositions, methods of manufacture, and uses thereof, and particularly relates to yellowness index of plastics.
Polyimides possess many desirable properties, such as, for example, high heat resistance, flame retardance, dimensional stability, strength, chemical resistance, biocompatibility, high dielectric strength, and transparence. Correspondingly, polyetherimide is employed for the manufacture of a wide-range of articles. Some of these applications include automotive applications (e.g., air intake manifolds, fluids handling, lighting applications, electrical connectors), medical applications (e.g., vascular infusion ports, luer connectors, stopcocks, dialysis filters), aerospace applications (e.g., interior semi-structural components, interior cladding, fluids handling, electrical connections), and electrical applications (e.g., electrical connectors, structural components). Furthermore, polyetherimide lends itself to most forms of thermoplastic processing and conversion, such as extrusion, injection molding, and the like. Although polyetherimides possess these, and other beneficial properties, it's utility can be hindered in some applications due to it's inherent amber color. This is especially the case in applications in which bright white colors are desired.
U.S. Pat. No. 3,957,526 to Hodgkin et al., is directed to titanium dioxide pigments and fillers, and teaches adjusting surface chemistry of the titanium dioxide, and using the titanium dioxide in polymers. Hodgkin et al. teach, among other things that, when the titanium dioxide with the modified surface is used in polymers, dispersion is faster and better in non-aqueous systems.
U.S. Pat. No. 3,971,755 to Zannucci et al. notes that polymer compositions which contain titanium dioxide pigment are sometimes more susceptible to photodegradation and are more difficult to stabilize against such photodegradation than are the unpigmented polymers. Zannucci et al. state that “the addition of 20% titanium dioxide (Ti-Pure R-100) to polypropylene reduces the lifetime to embrittlement of 5-mil thick films from 4 days to 1.5 days (irradiated at 65°-70° C. with 3000 A lamps).” (Col. 1, lines 31-35) Zannucci et al., therefore, address ultraviolet light stabilization of polymer compositions, and more particularly address ultraviolet light stabilization of titanium dioxide-pigmented polymer compositions. In a preferred embodiment of Zannucci et al., the titanium dioxide pigmented polymer is a polyolefin, and particularly a propylene containing polyolefin such as polypropylene or a polypropylene having grafted thereto acrylic acid or maleic anhydride or acid. The titanium dioxide is used in an amount of from 0.05 weight percent (wt %) to about 50 wt %, based on the weight of the polymer, with 0.5 wt % to 10 wt % titanium dioxide preferred in a molding composition, 0.1 wt % to 2 wt % titanium dioxide preferred in a fiber forming composition, and 5 wt % to 30 wt % titanium dioxide preferred in a coating composition.
U.S. Pat. No. 4,388,425 to Strehler et al. is directed to concentrates of titanium dioxide in polycaprolactam. Concentrates of from 20 wt % to 50 wt % of titanium dioxide in polycaprolactam are taught.
U.S. Pat. No. 5,256,728 to Dardaris et al. is directed to polycarbonate compositions comprising unpacified titanium dioxide. The amount of titanium dioxide employed is about 1 wt % to 20 wt % based on polycarbonate. Due to the redistribution of the polycarbonate, the titanium dioxide may be unpacified (i.e., titanium dioxide free from a polysiloxane coating). Dardaris et al. teach preparing a pigmented polycarbonate composition by melt equilibrating a linear or branched polycarbonate in the presence of a catalytic amount of a carbonate redistribution catalyst selected from the group consisting of bases and Lewis acids, to form a redistributed polycarbonate; and blending said redistributed polycarbonate with an amount effective for pigmentation of titanium dioxide free from polysiloxane coating.
U.S. Pat. No. 6,410,614 to Jones et al. is directed to incorporating titanium dioxide into materials such as polyamides, copolyamides, polyester, polyolefins, and polyurethanes. The titanium dioxide particles are present in an amount between about 60 wt % to about 70 wt % of the composition.
U.S. Pat. No. 6,607,794 to Wilson et al. is directed to light reflecting molded articles comprising a thermoplastic or thermoset polymer matrix in which is dispersed rutile titanium dioxide and a flame retardant material. They teach that the combined effects of the impurities in ABS and the opacity of rutile titania below 420 nanometers render the light reflected from the article somewhat lacking at the blue end of the visible spectrum. This problem may be addressed through the use of clear, transparent matrix polymers. Hence, polymers useful according to Wilson et al. comprise those with yellowness indices (YI) values of less than about 10, preferably less than about 5, and most preferably less than about 2.
There remains a continuing need in the art for improvements to produce bright white polymer compositions and products from yellow polymers. In particular, there is a continuing need for improvements to produce white polymer compositions and products wherein the yellow polymer has (either before or after processing), a YI (yellowness index) of greater than 11.